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The current standard of care for operable patients with early stage lung cancer has been well established as surgical resection +/- adjuvant chemotherapy, with local control rates close to 90%.

Treatment options for patients with inoperable early stage lung cancer are more limited. Local control rates for inoperable patients being treated with standard fractionation radiation therapy are dismal, and range from 30-50%.

Stereotactic body radiotherapy (SBRT) has emerged as an alternative treatment for patients with peripheral early stage inoperable NSCLC. It is both well-tolerated and effective, with local control rates similar to surgery for operable patients.

However, various recent studies on SBRT in lung cancer have reported the observation of increased chest wall pain and rib fractures in these patients.

At Princess Margaret Hospital, SBRT planning for patients with inoperable peripheral lung tumors is performed using 4D CT for construction of planning volumes. They use multiple non-coplanar beams, specifically 7 coplanar and 2 non-coplanar.

The purpose of this study was to retrospectively evaluate a subset of patients treated with high dose SBRT for the incidence of rib fractures and to examine associated dosimetric parameters.

Materials and Methods

This study is a retrospective review of a cohort of 42 patients with peripheral T1-2N0 NSCLC treated with 54-60 Gy in 3 fractions.

The median follow up was 11 months (2-35 month range).

The primary endpoint evaluated was a 2-year Kaplan-Meier (KM) estimate of rib fracture.

All patients had follow up CT scans inspected for fractures by both a radiation oncologist and radiologist. For patients who had a fracture, the CT scan was then fused with the planning CT scan dataset. The mean dose to the fracture site and maximum dose to 1 cc of the entire rib were calculated.

Results

42 patients were included in the current analysis.

Rib fractures were identified in 9 patients in the original analysis at an 11 month median follow up time. On a subsequent analysis, 2 additional patients were identified as having rib fractures as well.

In these 11 patients, a total of 18 ipsilateral rib fractures were identified.

For those 9 original patients with rib fractures, 2 were asymptomatic, 6 had moderate symptoms transiently, and 1 patient had severe toxicity requiring opiates and adjuvant analgesics.

Tumors were also found to be close to the chest wall (CW) for all of these patients, with a median distance of 0.4 cm (range: 0-1.8 cm) from the CW.

The 2-year Kaplan-Meier estimate of rib fracture rate in this group was 43%, with a wide 95% CI.

The median time to first fracture was 18 months (range: 7-30 months).

The median dose to the site of fracture was approximately 50 Gy. The authors suggested there may be a dose response relationship; however they have not made definitive conclusions on this at this time.

Author's Conclusions

The authors concluded that there is a significant risk of rib fractures for patients undergoing SBRT for tumors close to the chest wall.

It is critical that potential SBRT patients be given appropriate informed consent based on this information, and they should be made aware of the risks of rib fracture and associated symptoms.

The authors noted that although there is a significant risk of chest wall toxicity posed by SBRT, patients mostly had relatively mild to moderate symptoms, and the chest wall toxicity may be a reasonable trade-off for the increased local control rate provided by SBRT.

Clinical/Scientific Implications

This study provides important information for clinicians when discussing the risks and benefits of SBRT with patients.

This study shows that there is a significant risk of rib fractures seen for patients with peripheral lung tumors located close to the CW and treated with SBRT.

Although this risk is present, most patients have minimal toxicity associated with this, and the symptoms are often transient.

These patients have limited treatment options, and SBRT provides excellent local control, with rates approaching 90-95% at 2 years (Timmerman, et. al. 2006). As the authors duly noted, the benefits of improved local control with SBRT may outweigh the risk of the chest wall toxicity, especially since symptoms are minimal and transient.

However, thorough informed consent outlining the particular risks mentioned in this study is necessary for all patients who are candidates for SBRT.

The authors did also note that their rates of rib fractures were higher than outlined in a similar recent study by Petterson et al, presented at ESTRO 2007. Possible reasons for this may be higher doses to the involved areas or the use of more non-coplanar beams as compared to other studies.

Further dosimetric analysis on this subset of patients would be valuable. In addition, longer term follow-up is also necessary to observe late chest wall complications in these patients.